What are Tumbled Stones?
Tumbled stones are rocks and minerals that have been tumbled in a rock tumbler to produce smooth, rounded and highly polished stones that are exceptionally tactile. The process begins by placing stones of a similar size inside the barrel of the rock tumbler which is then filled with water, sand and coarse rock tumbling grit. The barrell then slowly rotates and in doing so the stones begin to lose their rough edges and over time take on a more rounded shape. The coarseness of the grit determines the smoothness of the stones so a coarse material is used initially and is then replaced with medium and then fine grit as the process continues. The grit works in a very similar way to sandpaper. The final stage of the tumbling process is to polish the stones which is done using grit that's almost as fine as powder.
The length of time that it takes to produce perfect tumbled stones can range from weeks to months and is dependent on factors such as the size of the rock tumbler which can vary from a small amateur machine up to something on an industrial scale, the size and texture of the rocks being used, the quantity inside the barrel and the type of grit that's used for the process.
Tumbled stones are created naturally as fragments of rock which are laying beneath or adjacent to a body of water are gently moved back and forth. The movement caused by the motion of the water causes them to rub against each other and against sediment which is made up of rocks, minerals and often the remains of plants and animals. Sediment can be as small as a grain of sand or as large as a boulder and sediment that's built up over millions of years is known as sedimentary rock. Over time the fragments of rock become smooth and take on a more rounded shape and then become known to us as beach pebbles or river pebbles. Rock tumbling is simply mimicking this process.
Industrial Sized Rock Tumblers
The vast majority of tumbled stones are minerals which are naturally occurring crystalline solids. A solid described as being crystalline means that it has a crystal structure or in other words is made up of crystals. This is how the word "crystals" (as in healing crystals) came about but it's worth mentioning that the term tends to only be used by people with an interest in crystal healing. Those whose interest in rocks and minerals is purely scientific rarely ever call them crystals.
The reason I said the "vast majority" of tumbled stones are minerals is because materials like obsidian, shungite and common opal are not actually minerals at all but are instead classified as mineraloids because they do not have a crystal structure. Likewise rocks cannot be described as minerals either because the vast majority are made up of more than one mineral. Many people use the term crystals, rocks and minerals interchangeably but they're actually all quite different. An example of a rock that's frequently tumbled is lapis lazuli, this blue coloured metamorphic rocks is made up of a number of different minerals so being pedantic, it shouldn't really be called a crystal or a mineral.
It really doesn't matter whether you refer to these naturally occurring solids as tumbled stones, minerals, healing crystals or simply crystals, these colourful and incredibly tactile stones have a wide variety of uses and are popular with rock and mineral enthusiasts of all ages. Being widely available and relatively cheap means that it's possible to build up a collection quite quickly and there's hundreds of different varieties to choose from.
Further information about creating your own tumbled stones can be found here.